Improving the efficiency of power plants is an ongoing process. This process assumes greater urgency in light of the threat of global warming. Power plants of the future must be as efficient as possible to reduce the amount of carbon dioxide emitted into the atmosphere. This is particularly important for power plants that burn coal because coal has a much higher carbon to hydrogen ratio than oil or natural gas and emits more carbon dioxide.
The U.S. has abundant coal resources which must be utilized to avoid large imports of oil and natural gas. Unfortunately, much of this coal contains contaminants of sulfur, nitrogen and particulate that cannot be released into the atmosphere. Therefore, it is important to identify ways of burning coal at the highest efficiencies without polluting the atmosphere.
To obtain high efficiency in a thermodynamic power plant, the working fluid must be heated to the highest temperature possible. Gas turbines of the current state of the art can utilize inlet temperatures of 2,350.degree. F. or above but only with clean fuels or heated air. Presently, steam power plants generally achieve turbine inlet temperatures of approximately 1,100.degree. F. Thus, current power plants which employ dirty fuel are not used to their full potential.
One approach to achieve optimal temperatures with coal is to gasify it and clean the coal gas prior to combustion. This approach is technically feasible but economically marginal because it is very difficult to gasify coal and clean coal gas.
Slagging furnaces are one approach to obtain high inlet temperatures. However, these furnaces are dirty, therefore they require expensive and elaborate controls to suppress pollution, which results in the furnaces being inefficient.
Fluidized bed reactors are known in the art for heating air in tubes up to temperatures of 1500.degree. F. However, if one attempts to obtain a higher heat in a fluidized bed reactor, pollution suppression in the bed is no longer feasible. Thus, fluidized bed reactors have not been successfully employed for obtaining high turbine inlet temperatures.